In inkjet printing, droplets of ink are selectively ejected from a plurality of drop ejectors (actuators) in a print head. The ejectors are operated in accordance with digital instructions to create a desired image on a print medium moving past the print head. The print head may move back and forth relative to the sheet in a typewriter fashion, or the linear array may be of a size extending across the entire width of a sheet to place the image on a sheet in a single pass. Additionally, multiple passes can be made to create a higher resolution image than the inherent resolution of the printhead.
The ejectors typically comprise a nozzle plate providing a plurality of nozzles, with each nozzle having drop ejection aperture (nozzle aperture), and one or more common ink supply manifolds. Ink supplied from the manifold travels through one or more tubes or conduits and is retained within a different channel for each ejector until there is a response by the ejector to an appropriate signal. In one embodiment of the ejector, the ink drop is ejected by a pressure change which results from a displacement of an electrostatically or magnetostatically actuated deformable membrane. The deformable membrane forms one electrode of a capacitor, with a counter electrode forming a second electrode. In MEMSJet technology, the nozzle plate and membrane can be manufactured from silicon. The nozzle plate can alternatively be made of a polymer layer with laser-drilled nozzle apertures. Each ejector further includes an ink cavity between the membrane and the nozzle plate. When the bias voltage is applied between the membrane and the counter electrode, the membrane deflects and increases the size of the ink cavity, which draws in a larger volume of ink. When the bias voltage is removed, the relaxation of the membrane pressurizes the fluid and causes a liquid drop to be formed and ejected out of the nozzle aperture onto a rotating drum, a moving belt, or paper.
This capacitor structure which incorporates the deformable membrane for silicon-based ejectors can be fabricated in a standard polysilicon surface micro-machining process as a micro electromechanical system (MEMS). A device can be batch fabricated at low cost using existing silicon foundry capabilities. The surface micro-machining process has proven to be compatible with integrated microelectronics, allowing for the monolithic integration of the ejector with associated addressing electronics.
It is desirable to dispense ink from the ejector at a temperature which is within a few degrees of a target temperature. For solid ink, the target temperature is typically between about 105° C. and 140° C. To assist in maintaining the ink temperature to within a tolerance of a desired temperature, the temperature of the print head is maintained using a relatively large block heater, for example comprising stainless steel, located on the print head which provides heating. Further, an inkjet device can comprise heaters wrapped around ink tubes leading to the print head.
New ways of providing improved control over the flow of dispensed ink from an inkjet print head, or another fluid in other fluid dispensing systems, would be desirable.